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Port Washington city arborist Jon Crain is on a mission — treating an estimated 600 city-owned ash trees for the emerald ash borer.

He began that task this week in the Spinnaker West subdivision on the city’s west side and doesn’t expect to finish it until July.

Crain selected 500 of the estimated 1,100 ash trees that line the city streets for treatment, as well as 100 in city parks, basing that decision on their size, species and overall condition.

The soil around smaller trees — less than 10 inches in diameter — will be injected annually with imidicloprid, while larger trees will receive trunk injections of emamectin bonzoate every other year, Crain said.

The roughly 250 soil treatments will take about a week to complete, he estimated, while the 240 or so trunk injections will take longer. He compared the trunk injections with intravenous treatments for humans, where the medication is slowly administered as the body absorbs it.

The treatments don’t pose any risk to the public, he stressed.

The city budgeted about $20,000 to treat its ash trees against the borer this year, with about half that amount being paid through a Department of Natural Resources grant, Public Works Director Rob Vanden Noven said.

The city’s action to treat its ash trees comes a year after the emerald ash borer — an invasive green beetle that has killed tens of millions of trees from the East Coast to the Midwest since 2002 — was first detected in Port Washington.

The borer was found in a dead ash tree on a wooded hillside in the 400 block of North Powers Street, and officials said several other dead trees in the area were likely killed by the insect.

The beetle infests all types of Fraxinus ash trees, including green, white and black ash, burrowing into the bark and laying eggs. The larvae hatch, then chew through the fluid-conducting vessels under the bark, cutting off the flow of water and nutrients to the tree and eventually killing it.

Crain said he believes the insect has been in the city for five to six years, a judgment he bases on research he’s done, discussions he’s had with the Department of Natural Resources, die back he’s seen in trees and the amount of woodpecker activity he’s seen.

“That (woodpecker activity) isn’t a tell-tale sign, but it’s a pretty good indication the borer is in a tree,” he said.

“A lot of trees, when they start showing signs, it’s too late.”

Mortality in trees generally spikes after the borer has been in a community for seven to eight years, so Crain said he expects the city will lose many ash trees in the next several years.

“I hope that’s not the case, but I’m seeing it more in our ravines and around the city,” he said.

Crain would not estimate how many ash trees in the city might be infested.

“I’ll know more and have a better assessment this summer,” he said, after the leaves have opened and the damage is more visible. “It’s really hard to say this early in spring.”

The city has taken down more than 30 trees infested with the borer, Crain said.

“I’m seeing a lot more that look suspicious,” he said.

The signs of the borer include dead branches near the top of a tree or wild, leafy shoots growing out of the lower trunk, D-shaped exit holes and bark splits that expose S-shaped tunnels and serious woodpecker damage as the birds eat the borer larvae in the trees.

Trees suspected of being infested with the borer can be found throughout the city, Crain said, as far north as Whitefish Road near Elephant Park and as far west as Melin Street.

Crain said he will be meeting with DNR officials in the coming weeks to discuss the situation, and they may help him get a better handle on it.

Image Information: PORT WASHINGTON city arborist Jon Crain injected a treatment against the emerald ash borer into the soil around a small ash tree on the city’s west side this week. Crain will spend the next month or so injecting treatments into the soil and trunks of about 600 city-owned ash trees to protect them from the borer, which was discovered in Port a year ago. Photo by Sam Arendt